Chassis rigidity

[Cam]

Hi guys,

I am about to strip back and paint the 'pan for my early ghia. I have already done the IRS/Balljoint conversion and got to thinking about different ways of making the chassis stiffer.

I was thinking of adding seam welds down the tunnel on either side/top & bottom.
MAYBE boxing in where the 13mm body-pan bolts go through.
And adding front beam braces.

Just wondering what you guys have had experience with and what else you could suggest?

Cheers,
Cam

[Southernbug]

I have seen some people box in the outer perimeter of the pan with rectangular tubing. In addition I think seam welding can help stiffen the pan but I still prefer spot welds.

The absolute best way to stiffen your chassis is to install a 6 point cage and tie is into the frame hours and front beam.

Rock on,

[Ghia Nut]

I have seen a bar mounted right behind the driver and passenger seat that crosses from passenger side to drivers side where harnesses can be tied up, I think it would also give some structural rigidity to the mid to back mid section of the car.



see what you think

I like it and will do it one day

[kdf]

The installation of the belts looks really nice on that ghia. But I don't think that it will add much stiffness to the chassis. Stiffening the chassis is the opposite to what many thinks, just removing or adding one tube from a stiff tube frame chassis can cause it to lose up to 30% of it's stiffness, and after that every additional tube that you remove after the first matters less.

I'd like to add that a 6 point roll cage with well thought out diagonals that is connected to the chassis in the right places throughout will add much stiffness compared to the weight added. There are roughly two kinds of roll cages, semi-structural and and not structural, both of them are safe and built according to rules, but only one of them contributes considerably to the chassis stiffness.

What you might want to think of and what might be of more importance is camber and toe stiffness of the suspension. Adding front beam braces is something very critical, when stock the front beam really moves around a lot.

[Rba]

Hi

I doing a turbo T4 conversion on my bug, and yesterday when i lifted the body off of the pan I began to think of different ways to make the pan stiffer. I will eventually add a rollcage, but right now I don't got the money or time to do it.
What I came up with was this:



I was thinking 25x25 mm tubing.

How do you think this will turn out? Will it be worth the effort and time?

/Rba

[Piledriver]

That isn't going to help chassis flex.
Take a sheet of paper, grab ot top and botton... Twist.
Pretty flexi...
2 or even 10 sheets of paper won't help much.

You have to think in 3 dimensions.

[helowrench]

Most of the engineering for additional chassis stiffness has been done already.

At the factory by factory engineers.

They did it for the convertible.

Research the different panels added to the convertibles, purchas or fabricate them, and install them.

I personally would seam weld everything, frame head, floor pans etc.
The longer the run, the more effective seam welds will be over spots.

But lets be realistic, the main forces in chassis flex are going to be twisting forces, around the horizontal plane. To combat this, you need to add in vertical stiffners in both remaining axis.
Kafer bar would help the rear quite a bit, and the front beam definitely needs something to attach the ends to the front outsides of the pan, and the firewall, I will have to look at that and ponder....

On another note the firewall itself will need to be reinforced, similar to the additional panels added into the vert bug. footroom suffers, but that's the price.

I will think some more, and see what I can think up.

BTW, the rear trailing arms absolutely must be boxed for any of this to be effective, too much room for side flex as it is.

Rob

[Bruce2]

I personally would seam weld everything, frame head, floor pans etc.
The longer the run, the more effective seam welds will be over spots.

Seam welding doesn't do a whole lot on a Beetle. It wasn't until the late 80s that the Japanese started doing the calculations
to determine how many and where to put spot welds. Their goal was the bare minimum since it takes time to do all those
welds. Their calculations don't include rally racing, so on those cars you really need to seam weld.

Our cars were built long before any consideration was done for the time needed to weld. They were also built by anal overkill
Germans.

I have several stress cracks in the body of my car. None of them originate at any spot welded joints.
A cage is by far the most effective way to stiffen up any car. If you don't want a cage, then the next best would be to install the
convertible rails under the heater channels.

[Ozzie]

anal overkill
Germans

So that's what Germany calls train drivers.

[Theo]

I autocross my 1969 Ghia and it is interesting that stiffening the chassis has not helped my times, in fact it may have lowered them.

Stiff is not necessarily good for road racing. Flex will keep the wheels on the ground. Very stiff may result in wheel lift. I may end up reducing my spring rates to get back the travel that the flex created.

The ridged chassis feels good to drive but I don't think it helps on the clock.

2 cents as always.

T